Froth breaking



P. MFRANTZ 2,3739

FROTH BREAKING iled July 20, 1939 I. 'i eff/alw Za Waffe ATTORNEYSPatented Apr. 20, v1943 ric FROTHBREAKING Philip Morliiser Frantz,Pueblo, Colo., assignor to The Colorado Fuel and Iron Corporation,Denver, Colo., a corporation of Colorado Application July 20, 1939,Seriali No. 285,488

14 Claims.

'Ihis invention relates to breaking froth and particularlymineral-bearing froths derived in ore dressing and the like.

In the concentration of minerals by froth flotation, a froth is formedwhich comprises gasfilled bubbles coated with a film of collecting agentwith mineral particles adhering thereto. The froth usually is formed byaeration of an aqueous suspension or pulp of a mineral aggre'- gate inthe presence of one or more otation agents which usually are of soapy oroleaginous character. The froth forms on top of the pulp and is removedtherefrom by simple overflow or by skimming or sluicing. The frothusually contains considerable entrained water.

, The froth, once it is separated from the pulp, ordinarily is subjectedto further treatment including a. de-watering or filtration operation.If the froth is very tenacious and resists destruction by agitation andthe like, de-watering, ltration and other subsequent operations areconducted with difficulty. Thus, a persistent froth may result in anunsatisfactory lter cake.

'Ihe froth formed in the otation of fine coal and other non-metallicminerals is oftemmost tenacious and is de-watered or otherwise treatedto reduce its bulk with great difficulty. As a result of myinvestigations, however, I have discovered that the incorporation of astarch emulsion into tenacious froths results in destruction of bubblesand in conditioning the froth so that even upon subsequent aeration thebubbles do not re-form to a substantial extent.,V I have found, further,that froths so treatedare much more amenable to filtration and the like,

Thus, in a process involving the formation of a froth comprisinggas-filled bubbles coated with a collecting agent to which mineralparticles adhere, my invention contemplates breaking said froth byincorporating an aqueous lstarch emulsion therein. I have found,further, that the presence of an acid or base in the emulsion, so thatthe latter is not neutral and has a pH othe'i` than 7, aids greatly infroth breaking.

The emulsion is made conveniently by boiling flour or other material ofhigh starch content in c Water, and thereafter adding to the resultingpastean acid or base. Any suitable water-soluble base, such as alkalimetal hydroxides, ammonium hydroxide, or calcium hydrate may be employedployed. Thus, I have found that acetic acid, strong mineral acids, suchas nitric acid, hydrochloric acid, and sulfuric acid, and organic acids,and acid-containing substances such as cresylic acid, creosote, taracids and crude or refined phenols, may be used advantageously.

I have found further that a' starch of high I amount of flotationreagent present in the froth.

The reagent apparently reacts in some way with most oleaginous or soapyconnecting agents to form new compounds which do not tend to maintainfroth. In 4any case, as the amount of otation reagent in thefroth isincreased, the amount of froth breaking reagent needed must also beincreased, but an excess of froth breaking reagent over and abovethatnecessary to accomplish adequate froth destruction does not result inimprovement and represents a waste. 'I'he amount of froth breakingreagent necessary will vary somewhat depending upon the'nature of theflotation reagent employed. Generally speaking. however, the proportionof froth breaking reagent necessary is always less than the flotationreagent consumed, and, in fact, the amount of starch employed in frothbreaking need not exceed r of the weight of the collecting agentconsumed.

These and other aspects of my invention will be more thoroughlyunderstood in the light of the following detailed description ofpresently preferred practices thereof, taken in conjunction with theaccompanying single gure which is a flow sheet of a coal ilotationoperation embodying the practice Iof my invention. n v

Referring now' to the ligure, it will be observed that an aqueous pulpI0 of fine coal mixed with gangue material and a large proportion ofwater (derived from customary coal washing operations) is passed to aDorr thickener I I of conventional constructiom The coal andcontaminating gangue materials tend to settle in the thickener and areremoved as a thickened underflow I2. An aqueous overow I3 containingsubstantially no coal is derived from the thickener and sent to waste.

The coal-bearing underflow from the thickener is sent to a. coalflotation apparatusV I4 which may be any suitable froth flotationmachine and is there agitated and aerated by' -oleaginous character, arealso introduced into the flotation machine and a coal-.bearing froth i1is formed in the conventional manner. The froth is removed from theflotation machine by sluicing or skimming and the tailings I8 pass outof the machine and are sent to waste.

VA great variety of oleaginous or soapy flota'- tion agents may beemployed in the treatment of the coal. In one instance, the flotationreagent employed was a paraflin base crude oil diluted with kerosene towhich had been added 10% by weight of creosote. Another suitable reagentcomprises coal tar distillate having a gravity of about .825 to which isadded 5% by Weight of tar acids. Such reagents may be employed appropriately in the treatment of a coal-bearing pulp containing about 18%solids having the following screen analvsis:

- the pulp.

As indicated hereinbefore, a great variety 'of lli-sh Weight feighllatir@ weight Pcrcen! Per ccnl 11H-35. Y Y l0. 0 3. 42 3. 76

10U-H501.. 26.0 8.90 49.56 ,l50+200. l.. 20.2 6.85 56.41

boiling onepart =-of flour, preferably 'of high protein content, in 100parts of water. To this boiling mixture, there is added one-half part of.Y

an acid or alkali (say acetic acid or sodium hydroxide) in a hotconcentrated aqueous solution.

Very small proportions of such an emulsion are necessary for adequatefroth destruction. Thus, I have found that with froth formed in theforegoing manner it is sufficient to employ about .13 lb. of flour and.065 lb. of ton of solids in the froth.

The ratio of starch to water and'caustic or acid employed is notcritical. However,in general, it will be found that an emulsion made ofone part of flour or starch, 100 parts of water and caustic 'per aboutone-half part of acid or alkali will -pro duce a verysatisfactoryreagent and one which isV thin' enough toY be incorporated easily Aintoalkalies and acids may'be employed. I have found that the best reagentsto employ with the starch or flour are, in the order of theireiliciency, caustic soda, acetic acid and crude creo- Y sote. v

it flows, usually with additional sluicing water. in a launder from theflotation machine. Good results may also be obtained by introducing alarge batch of the froth into a tank into which the froth-breakingreagent is also introduced. the whole being agitatedpfor a short periodof time, say ve minutes. Ordinarily,'however, it is better to break thefroth in a continuous operationby passing it continuously through asmall agitator I9 to which the froth-breaking reagent 20 in. appropriateproportion is continuously supplied.

As indicated hereinbefore, the higher the protein content of the starchwithin limits, the more effective is the froth-breaking reagent in whichthe starch is incorporated. Thus, I have found that bean fiour made byVcomminution of navy beans and containing about 22% protein isapproximately twice as effective in frothbreakingfas is a low-gradewheat flour containing about 12% protein, and in the practice of theinvention, I prefer to employ a material containing at least 10% ofprotein on the weight of the starch.

The use of the froth-breaking reagent in the treatment of flotationpulps` results inA a great improvement in ltration operations conductedupon the solids present in the froth. Thus, I have found that when thecoal froth made as described hereinbefore is treated on a continuousfilter withoutuse of the frotl'vbreaking reagent. a very soft wet cakeis formed and the filtration rate is very slow. The resulting cakecontains about 39% moisture. On the other hand, when .an identical frothis treated on identical apparatus after incorporation of thefroth-breaker, I find that the broken froth filters approximately fourtimes as fast and forms froths containing rock phosphates, fluorspar, or

other non-metallic minerals. However, the process of my invention isalso applicable to the destruction of flotation froths of minerals ofmetal- 'lic' surface. such as those derived from the concentration ofsulfide ores of copper, zinc. and the like. But the collecting agentsemployed in the notation of sumdes. and the like, seldom result in atenacious froth.

I have found that, generally speaking, acid froths or froths derivedfrom acid pulps break more easily than do froths derived from basic orneutral pulps. Likewise, alkaline froths or froths derived from alkalineVpulps break more 6d easily .than do neutral pulp's. Consequently, for

most effective practice 'of my invention, the pulp from which the frothis derived should be maintained with a pH that is definitely off theneutrai point, i. e., above or below 7. and the frothbreaking reagentshould be acid in the event that the pulp is acid and vice versa.However, the amount of froth-breaking reagent employed is ordinarilyinsufficient to bring about any substantial change in* the pH of .thefroth.

As shown in the flow sheet, coal slurry 2| resultingfrom incorporationof the froth-breaking reagent in the froth is subjected to filtration`on a filter 22 such, for example, as an Oliver filter,

.a Dorrco filter, or an American leaf-type filter. Filter cake 23 fromthis operation is subjected: i

to drying in any suitable dryer 24 and the dried fine coal 25 is readyfor market.

I claim:

1. In a process involving the formation of a froth comprising gas-filledbubbles coated with a collecting agent to which mineral particles areadhering by aeration of an aqueous mineralbearing pulp containing thecollecting agent, the improvement which comprises incorporating in saidfroth an aqueous starch emulsion of high protein content and therebydestroying the froth.

2. In a process involving the formation of a froth comprising gas-filledbubbles coated with a collecting agent to which mineral particles areadhering by aeration of an aqueous mineralbearing pulp containing thecollecting agent, the improvement which comprises incorporating in saidfroth an aqueous starch emulsion having a protein content of at least onthe weight of the starch.

3. In a. process involving the formation of a froth comprisinggas-filled bubbles coated with a collecting agent to which mineralparticles are adhering by aeration of an aqueous mineralbearing pulpcontaining the collecting agent, the improvement which comprisesincorporating in said froth an aqueous starch emulsion derived from beanflour.

4. In a process involving the formation of a froth comprising gas-filledbubbles coated with a collecting agent to which mineral particles areadhering by aeration of an aqueous mineral-f. bearing pulp containingthe collecting agent, the improvement which comprises incorporating insaid froth an aqueous starch emulsion derivedv from wheat flourcontaining at least 10% by weight of protein.

5. In a process involving the formation of a froth 'comprising gas-lledbubbles coated with a collecting agent to which mineral particles areadhering by aeration of an aqueous mineralbearing pulp containing thecollecting agent, the improvement which comprises incorporating in thefroth an alkaline aqueous starch emulsion.

v6. In a process involving the formation of a froth comprisinggas-filled bubbles coated With a collecting agent to which mineralparticles are adhering by aeration of an aqueous mineralbearing pulpcontaining the collecting agent, the improvement which comprisesincorporating in said froth an acid aqueous starch emulsion.

7. In a process involving the formation of a froth comprising gas-lledbubbles coated with a collecting agent to which mineral particles areadhering by aeration of an aqueous mineral-- bearing'pulp containing thecollecting agent, the improvement which comprises incorporating in saidfroth an aqueous starch emulsion containing alkali metal hydroxide.

8. In a process involving the aeration of an aqueous mineral-bearingpulp in the presence of a collecting agent to form a froth comprisingair-filled bubbles coated with the collecting agent to which the mineralparticles are adhering and the separation of said' froth from said pulpIthe improvement which comprises subsequently subjecting said froth tothe action of an aqueousstarch emulsion.

9. In a process involving the aeration of an aqueous mineral-bearingpulp in the presence of a collecting agent to form a froth comprisingair-filled bubblesv coated with the collecting agent to which themineral particles are adhering and the separation of said froth fromsaid pulp, the improvement which comprises subsequently incorporatinglin said froth an aqueous starch emulsion and thereafter subjecting theresultant product to filtration.

10. In a process involving the aeration of an aqueous mineral-bearingpulp in the presence of a collecting agent to form a froth comprisingairfilled bubbles coated with the collecting agent to which the mineralparticles are adhering and the separation of said froth from said pulp,the improvement which comprises maintaining a pH other than 7 in saidpulp and incorporating in the froth after separation an aqueous starchemulsion.

11. In a process involving the aeration of an aqueous mineral-bearingpulp in the presence of a collecting agent to "form a froth comprisingalrlled bubbles coated with a collecting agent to which the mineralparticles are adhering and the separation of said froth from said pulp,the improvement which comprises subsequently adding an aqueous starchemulsion to said froth and subjecting the resultant mixture to agitationto distribute the emulsion therethrough.

12. In a process involving the-aeration of a mineral-'bearing pulp inthe presence of an oleaginous collecting agent to form a frothcomprising air-filled bubbles coated with the oleaginous agent to whichmineral particles are adhering, the improvement which comprises treatingthe froth after separation thereof from the pulp with an aqueous starchemulsion having a pH other than 7.

13. In a vprocess involvingthe aeration of a 'mineral-bearing pulp inthe presence of a collecting agent with resultant formation of a frothcomprising gas-filledv bubbles coated with the collecting agent to whichthe mineral particles adhere, the improvement which comprisesincorporating in the froth after separation from the pulp an aqueousstarch emulsion, the weight of starch in the emulsion thus incorporatedbeing substantially less than the weight of the collecting agentemployed.

14. In a process involving the formation of a froth comprisinggas-filled bubbles coated with a collecting agent to which mineralparticles are adhering by aeration of an aqueous mineralbearing pulpcontaining the collecting agent, the improvement which comprisesincorporating in said froth an aqueousv starch emulsion containing astrong mineral acid.

PHILIP MORHISER FRANTZ.

